The invention relates to compositions and methods for reducing susceptibility to infectious disease in bees using RNA interference technology, and more particularly, to the use of dsRNA for prevention and treatment of viral infections in honeybees.
Colony Collapse Disorder
The importance of honeybees and other pollinating insects to the global world economy far surpasses their contribution in terms of honey production. The United States Department of Agriculture (USDA) estimates that every third bite we consume in our diet is dependent on a honeybee to pollinate that food. The total contribution of pollination in terms of added value to fruit crops exceeds $15 billion per annum, with indirect potential consequence of $75 billion dollars.
Viral Diseases in Honeybees
The health and vigor of honeybee colonies are threatened by numerous parasites and pathogens, including viruses, bacteria, protozoa, and mites, each with characteristic modes of transmission.
In general, transmission of viruses can occur via two pathways: horizontal and vertical transmission. In horizontal transmission, viruses are transmitted among individuals of the same generation, while vertical transmission occurs from adults to their offspring. Transmission can occur through multiple routes in social organisms (for a detailed review see Chen Y P, et al (2006) Appl Environ Microbiol. 72(1):606-11). Recently, horizontal transmission of honeybee viruses has been documented in bee colonies, for example, transmission of deformed wing virus (DWV) and Kashmir Bee Virus (KBV) by the parasitic mite Varroa destructor, as well as some evidence of virus in honeybee eggs and young larvae, life stages not parasitized by Varroa mites. Vertical transmission of multiple viruses from mother queens to their offspring in honeybees has also been recently demonstrated, as well as viruses in feces of queens, suggesting a role for feeding in virus transmission. Moreover, honeybee viruses have been detected in tissues of the gut, suggesting that viruses could be ingested by queens from contaminated foods and passed into the digestive tract, which then acts as a major reservoir for viral replication. Indeed, viruses might penetrate the gut wall and move into the insect hemocoel, spreading infections to other tissues.
In honeybees viruses often persist as latent infections. Thus, group living activities such as trophylaxis and nurse bee brood feeding, can potentially drive high levels of horizontal transmission or amplification of existing infections.
Colony Collapse Disorder
Colony Collapse Disorder (CCD) of honeybees is threatening to annihilate U.S. and world agriculture. Indeed, in the recent outbreak of CCD in the U.S in the winter of 2006-2007, an estimated 25% or more of the 2.4 million honeybee hives were lost because of CCD. An estimated 23% of beekeeping operations in the United States suffered from CCD over the winter of 2006-2007, affecting an average of 45% of the beekeepers operations. In the winter of 2007-2008, the CCD action group of the USDA-ARS estimated that a total of 36% of all hives from commercial operations were destroyed by CCD.
CCD is characterized by the rapid loss from a colony of its adult bee population, with dead adult bees usually found at a distance from the colony. At the final stages of collapse, a queen is attended only by a few newly emerged adult bees. Collapsed colonies often have considerable capped brood and food reserves. The phenomenon of CCD was first reported in 2006; however, beekeepers noted unique colony declines consistent with CCD as early as 2004. Various factors such as mites and infectious agents, weather patterns, electromagnetic (cellular antennas) radiation, pesticides, poor nutrition and stress have been postulated as causes. To date, control of CCD has focused on varroa mite control, sanitation and removal of affected hives, treating for opportunistic infections (such as Nosema) and improved nutrition. No effective preventative measures have been developed to date.
That CCD is due to the introduction of a previously unrecognized infectious agent is supported by preliminary evidence that CCD is transmissible through the reuse of equipment from CCD colonies and that such transmission can be broken by irradiation of the equipment before use.
Recently, Israeli acute paralysis virus of bees (IAPV, SEQ ID NO: 6), was strongly correlated with CCD. Indeed, Table 1 below shows that although other etiological agents of diseases in honeybees were found in CCD colonies, many were also found in apparently healthy, asymptomatic operations. In contrast, IAPV was not only found in 83% of CCD colonies, but was almost completely absent from apparently healthy colonies.
TABLE IAnalysis of bees tested for pathologicalcandidates in CCD and non-CCD operationsPositveCCDNon-CCDTotalpredictiveAgent(n = 30)(n = 21)(n = 51)value (%)IAPV25(83.3%)1(4.8%)26(51.0%)96.1KBV30(100%)16(76.2%)46(90.2%)65.2N. apis27(90%)10(47.6%)37(72.5%)73.0N. ceranae30(100%)17(80.9%)47(92.1%)63.8All four agents23(76.7%)0(0%)23(45.0%)100IAPV—Israel Acute Paralysis Virus; KBV—Kashmir Bee Virus; N. apis—Nosema apis; N. ceranae—Nosema ceranae.From: Diana L. Cox-Foster et al. (2007) A Metagenomic Survey of Microbes in Honey Bee Colony Collapse Disorder; Science 318: 283-286.
Moreover, it was recently shown that when injected or fed to the bees, IAPV causes paralysis and death in 98% of bees within days, further confirming IAPV as the infective agent in CCD.
Israeli acute paralysis virus (IAPV) has been characterized as a bee-affecting dicistrovirus. Recently, DNA versions of genomic segments of non-retro RNA viruses have been found in their respective host genomes, and the reciprocal exchange of genome sequences between host and virus has been demonstrated (Maori et al. Virology 2007; 362:342). These authors showed that the bees who harbored integrated viral sequences were found to be resistant to subsequent viral infection, and a RNAi mechanism of resistance was postulated. Most recently, as shown in Table 1 above, a metagenomic survey has indicated a close association between CCD and IAPV (Cox-Foster et al., Science, 2007; 318:283).
It thus follows that prevention of IAPV infection may prevent development of CCD, significantly improving the state of the beekeeping industry and world agriculture. The United States Department of Agriculture has developed an urgent action plan intended to cover all aspects of bee management to combat CCD and avoid future threats to honeybee management. They seek to maintain bees with resistance to parasites and pathogens and develop new methods of managing parasites and pathogens (see “CCD_actionplan” at the USDA website). However, no specific measures have been recommended, other than improving general sanitation, nutrition and combating opportunistic infections.
Methods for Silencing Using siRNAs/dsRNA
RNA interference (dsRNA and siRNA) has been shown effective in silencing gene expression in a broad variety of species, including plants, with wide ranging implications for cancer, inherited disease, infectious disease in plants and animals. It was also shown in a variety of organisms that dsRNA or their siRNA derivatives can be used to arrest, retard or even prevent a variety of pathogens, most notably viral diseases (see, for example, WO/2003/004649 to Tenllado et al).
It has been shown in some species that RNAi mediated interference spreads from the initial site of dsRNA delivery, producing interference phenotypes throughout the injected animal. Recently the same spreading effect of dsRNA has been demonstrated in bee larva, as well as detection of SID transmembrane channels considered responsible for endocytic uptake and spreading effect of dsRNA in humans, mouse and C. elegans (Aronstein et al, J. Apic Res and Bee World, 2006; 45:20-24).
Application of interference RNA technology for insects that are plant pests and other plant pests has been suggested. Moderate RNAi-type silencing of insect genes by feeding has been demonstrated (Turner et al., Insect Mol Biol 2006; 15:383; and Araujo et al., Insect Mol. Biol 2006; 36:683). dsRNA absorbance via honey has also been demonstrated (Aronstein et al., J Apiculture Res Bee World 2006; 45:20-24).
U.S. Pat. No. 6,326,193 refers to the use of recombinant insect viruses such as baculoviruses expressing dsRNA to silence selected insect genes for pest control. PCT application WO 99/32619 describes generally that dsRNA may be used to reduce crop destruction by other plant pathogens or pests such as arachnids, insects, nematodes, protozoans, bacteria, or fungi. PCT patent application WO 2004/005485 describes the use of vectors comprising sequences designed to control plant-parasitic nematodes by RNA interference, and transgenic plants transformed with such vectors. US patent application 20030180945 generally describes chimeric genes capable of producing antisense or sense RNA equipped with a prokaryotic promoter suitable for expression of the antisense or sense RNA in a particular prokaryotic host.
US Patent Application 20030154508 describes a method for pest control comprising exposing said pest to a compound (dsRNA) which disrupts, within said pest, a cation-amino acid transporter/channel protein.
PCT patent application WO 02/14472 describes methods for inhibiting target gene expression in a sucking insect, by expressing in a cell a nucleic acid construct comprising an inverted repeat and a sense or antisense region having substantial sequence identity to a target gene, wherein the inverted repeat is unrelated to the target gene. US patent application 20030150017 describes the use of RNA molecules homologous or complementary to a nucleotide sequence of a plant pest such as nematodes and insects.
Raemakers et al (PCT Applications WO 2007/080127 and WO 2007/080126) have disclosed transgenic plants expressing RNAi for controlling pest infestation by insects, nematodes, fungus and other plant pests. Among the sequences taught are sequences targeting essential genes of insects, including the honeybee. Waterhouse et al (US Patent Application 2006 0272049) also disclosed transgenic plants expressing dsRNA, and dsRNA directed to essential genes of plant insect pests, for use as insecticides, particularly against sap-sucking insects such as aphids. Boukharov et al. (US Patent Application 2007 0250947) disclosed constructs for expressing dsRNA in transgenic plants for targeting plant parasitic nematodes, specifically the soybean cyst nematode. While expression and processing of dsRNA were demonstrated, no actual inhibition of infestation with the dsRNA was shown.